The biogenesis of mitochondria in higher and lower eucaryotes depends on the expression of two separate sets of genes, one located in the nucleus and the other in the organellar genome. The gene products of mitochondrial DNA have been well characterized in yeast and in some mammalian systems. The DNA sequence analysis of the yeast and human genomes has provided a wealth of new information about the molecular organization as well as some of the unusual coding properties of these DNAs. The present proposal represents an attempt to further clarify the mechanisms by which the genes of yeast mitochondrial DNA are transcribed and the messengers matured. A second important area of studies is concerned with the nature of nuclear regulation of specific gene regions on mitochondrial DNA. Two approaches will be used to study transription of the yeast genes. The first is to characterize the messengers and large precursor transcripts of the ATPase and apocytochrome b genes. The messengers will be sequenced and the processing signals identified by Norther blot analysis of the precursor RNAs. The second approach will entail the isolation of processing enzymes that catalyze the cleavage and ligation reactions leading to messenger maturation. To study the regulation of mitochondrial genes, a project has been initiated to saturate all the nuclear genes of yeast required for the morphogenesis of functional mitochondria. This collection of strains will be screened by biochemical methods for regulatory mutants. Once appropriate mutants are obtained, the genes will be cloned and the effect of the putative products on transcription and/or translation of mitochondrial genes examined. The objective of these studies is to define the nuclear products that influence the coordinate expression of the mitochondrially and nuclearly encoded subunits of the ATPase and coenzyme QH2-cytochrome c reductase.